The present invention relates to dispensing syringes for simultaneously discharging a plurality of reactive fluids. Syringes of this type are generally designed to dispense liquid or semi-liquid materials in a predetermined ratio. Materials requiring this mode of application include reactive, two-component adhesives, sealants, and coatings, as well as co-dispensed materials combining an adhesive or sealant and a colorant paste. Typical materials formed from reactive multi-component mixtures include epoxies, acrylics, silicones, polyesters, and urethanes.
Devices for simultaneously dispensing such reactive materials, particularly for smaller quantities of materials for use in consumer applications, typically comprise a syringe having two parallel, cylindrical bores or barrels filled with the reactants, with two joined plungers or pistons that fit into the barrels. In the filled and assembled device, the plungers are pre-fitted into the barrels to seal the contents until use. In use, the plungers are manually forced into one end of the bores to cause the materials to flow out a nozzle or nozzles at the other end of the bores. The nozzle or nozzles are sealed with frangible or removable seals molded or fitted on the nozzle ends, which are severed or removed by the user to permit the barrel contents to flow out. A cap or other resealing apparatus is provided to re-seal the nozzle or nozzles until the next use.
In order to form a uniformly composed cured product, the dispensed components must be adequately mixed to form a homogeneous reaction mixture. Simpler devices having separate nozzles for each reactant require the user to mix the dispensed components in-situ on the application site, or on a separate mixing site prior to application, using a stirring rod or other suitable mixing tool, which may double as an applicator. This approach, while keeping the dispenser simple, is not always practical for dispensing small quantities in a precise manner as called for frequently in consumer applications. The user typically has to dispense more than is needed for the application, leading to waste. The excess material also presents hazards due to spillage, contamination, exposure, and disposal.
In an alternate approach, the dispensing syringe is provided with a static mixing element that fits onto the open nozzle or nozzles. The mixing element forces the reactive components into an intimate mixture that can be applied directly from an exit nozzle on the mixer. This type of device significantly improves the ability of the user to meter and precisely apply small quantities of the reactive mixture, while at the same time significantly reducing the hazards associated with manual mixing. The static mixing element can only be used for a single application, since the reactive mixture within it cannot be flushed and will cure to clog it permanently. On the other hand, the syringes are nearly always filled with a sufficient quantity of reactants for more than one application. Therefore the devices are sold in a single package with two or more disposable static mixers for multiple uses.
A recurrent issue with these systems involves the inadvertent separation of the syringe assembly from an unused static mixer. Of necessity the mixers are separate or separable from the syringe assembly so to be attached to the open nozzle or nozzles. The risk exists that during use or subsequent storage the unused static mixer will become permanently separated from the syringe assembly and thereby impair the system's utility. A related problem is the loss of the cap or other re-sealing means to preserve the reactants for subsequent applications while the system is stored prior to re-use. For simplicity the cap is often frangibly molded together with the syringe body or plunger assembly and is broken off for use. The small size of the caps renders them particularly susceptible to misplacement and loss, exposing the contents of the barrels to degradation and spillage.